Tag Archives: genetics

Atlantic salmon (Salmo salar) as their name implies, are primarily found in northern Atlantic waters and are classified as androminous (living in the sea, and returning to freshwater to spawn). Known to be a popular recreational sport fish, this largest species found in the genus Salmo is prized for its table fare and thus, faces heavy commercial fishing pressure. This species is particularly sensitive to habitat alteration and human influence (Staurnes et al. 1995; Kroglund et al. 2007) and coupled with the high commercial demand, has seen significant historical declines over the last half century. These declines have led to substantial increases in aquaculture farming techniques where salmon are raised in pens on the very same waters utilized by native, wild populations to spawn. Breeding and farming programs have greatly altered the genetic makeup of Atlantic salmon as commercial enterprises target specific characteristics such as: larger total size, faster growth rates, efficient food utilization, and meat quality. But what happens to the inevitable large quantity of farm “escapees”?

Atlantic salmon are popular sport fish in Norway and beyond [Image by Vetle Kjærstad]

A recent study by Diserud Karlsson and others investigated and quantified genetic introgression (genetic mixing or “hybridization”) of escaped farmed to wild Atlantic salmon. Extracting genetic material from either scales or fin clips, and using several specific genetic markers representative of both wild and farm raised individuals; the team was able to quantify genetic introgression in 147 salmon rivers in Norway. A study of this magnitude was able to account for and represent three quarters of the total wild spawning population in the entire country. What the team found was an average level of genetic introgression of 6.4%, within a total range of 0.0% to as high as 42.2%. Moreover, significant genetic introgression had occurred in 51 separate wild salmon populations, with significant genetic introgression also occurring in 77 of 147 sampled rivers.

So why is the genetic introgression or “mixing “of farmed salmon to wild salmon ecologically important? The main concerns by the authors regarding genetics are the loss of genetic variation within a population, the loss of genetic variation between populations, and the loss of overall animal ecological fitness. It has long been shown that farmed salmon have much lower genetic variation compared to their wild counterparts ((Mjølnerød et al. 1997; Skaala et al. 2004, 2005; Karlsson et al. 2010). In addition, substantial loss of ecological fitness has been documented in farm-raised salmon. If wild to farmed genetic introgression continues at this rate, it is feared wild salmon populations will too lose genetic attributes, all of which are critical in sustaining healthy, disease-free, wild salmon populations.

This research has real-world applications, as many hydropower companies that alter the natural state of rivers, and reduce natural productivity of native salmon compensate this “offset” by releasing farm raised fish into the river system. In the western United States, native cutthroat trout are facing a similar threat, as genetic introgression with rainbow trout is occurring at a rapid rate. It has been proposed to list the few remaining genetically “pure” populations of cutthroat trout under the Endangered Species Act (ESA). Similar proposals have been made to Atlantic salmon, even going so far as to list farm-raised salmon a different species, and treating farm raised “escapees” as an exotic species, to help deter genetic hybridization and introgression with wild populations.

One positive finding within the study was the lowest genetic introgression rates were located within Norwegian nationally protected lands (National Salmon Rivers and National Salmon Fjords), thereby demonstrating the ecological importance of preserved lands to wildlife populations. Indeed, there is no clear, sound solution to this problem, especially as the numbers of salmon farms are increasing globally. However, it is clear that at the present time, near-zero limits are the only viable solution to protect the genetic integrity of wild Atlantic salmon populations.

Minke whales, Balaenoptera acutorostrata, may not be the largest baleen whale, but they are the most abundant. These whales are about thirty five feet long, 6500kg, and are black with a white stomach (Knox, G.A., 2007). This species of whale is said to be a cosmopolitan species, since they are found in many different climates of the world. Although these whales are abundant, one of their main threats is overexploitation in fisheries. In places, such as the North Pacific, their populations have been fished so much that the International Whaling Commission, the IWC, has them listed as of concern. Overfishing is not the only threat to minke whales. They are also threatened by noise, vessel strikes, and habitat disturbance. (Minke Whale, 2014).

A minke whale.

Like many other marine mammals, minke whales have multiple techniques to catch their prey. Minke whales feed on a variety of food. These varieties are crustaceans, plankton, and small schooling fish. In order to eat some of these food types they must dive. This species can dive for up to fifteen minutes at a time. Some of the techniques that they use while diving include landing on their side on top of the prey and ingesting a significant amount of water while feeding. By side lunging they can stun their prey and by gulping a lot of water they can collect a lot of plankton that they can then sift through (Minke Whale, 2014). Once they have the food, minke whales then swallow their food whole (Know, G.A., 2007). Diving for their prey requires a lot of adaptations.

When a whale dives, a lot of changes occur internally. There are three steps that occur when marine mammals hold their breath. The first step is called hypoxia, which is the decrease in oxygen in the whale’s body. The second step is hypercapnia when the body experiences an increase in carbon dioxide. And the final step occurs when there is a build up of lactic acid in the body. All of these stages add up and prevent the animal from suffocating because they tell the body that it needs air. Thus, the whale then returns to the surface to breathe (Richardson, 2013). One of the main behaviors of minke whales is diving, and a recent study on their genetics shows how their genes are adapted for this behavior.

Minke whales provide a good specimen for genome sequencing because they are such a widely distributed marine mammal. This study is the first of its kind to complete a high depth genetic analysis of a marine mammal. From the study, the researchers found that there were many whale specific genes. One of the most interesting gene that was found to be expanded in minke whales was the peroxiredoxin (PRDX) family. This family is related with stress resistance. The fact that this gene family is expanded could show that these animals are prone to stress, whether from humans or from diving, and have evolved to have more stress combating genes. Another interesting finding also involved their diving physiology. O-linked N-acetylglucasominylation in many proteins has been found to multiply the response to stress. Stress occurs when a minke whale dives and experiences hypoxia. In minke whales, this gene is expanded three times. This gene is just an example of one of the many genes they found expanded that are related to dealing with hypoxia. In addition, as mentioned above, lactate can build up in the body after prolonged diving. The researchers found that the enzyme, lactate dehydrogenase, which converts pyruvate to lactate to be expanded in animals, such as minke whales. Therefore, many different objects in the minke whale genome have expanded in order to account for the behaviors most exhibited by this animal. This study was very ground breaking and will lead the way for many other marine mammal genomes to be completely sequenced (Yim, H et al, 2014).